It is already known to upgrade split or leather hides having an injured surface by applying a coating in the form of a prefabricated film of synthetic plastic material. For this purpose, an adhesive is applied to the split, whereupon the film is placed thereon and glued to the split with a heated press. In this connection it is known to arrange within the press an embossing metal sheet for giving the film of synthetic plastics material during pressing a grain structure. For this purpose the film must be softened and the temperatures prevailing within the press are thus substantially elevated temperatures of approximately 170.degree. C. Under the influence of these temperatures as well as under the influence of the compressing forces exerted within the press, the leather is strongly affected and is strengthened in an undesired manner.
It has also been proposed to use a high frequency plate press equipped with a mold of silicone rubber for glueing the film of synthetic plastics material to the split. The leather coated with an adhesive and having the film arranged thereon are, in this case, put into the cold mold of silicone rubber, whereupon high frequency heating is effected. Because the leather always containing moisture, the leather is also heated by the high frequency field and the above-mentioned drawbacks are thus not overcome.
Additionally, there is already known a process for dressing split in which the coating to be bonded to the split is formed from a polyurethane dispersion having incorporated therein hollow microspheres or compact particles containing an inflating agent and forming hollow microspheres when heat is supplied to them, the shells of the hollow microspheres have enclosed therein a gas and preferably consisting of a vinylidene chloride copolymer. The aqueous dispersion of a polyurethane is, in this case, applied either directly onto the latter to be coated or onto a removable supporting surface noting that in the latter case the leather is place on top of a layer of a polyurethane dispersion. The polyurethane dispersion is then allowed to solidify and any supporting surface is removed. With this known process, drying of the polyurethane dispersion applied onto the leather can be effected, for example, by means of a vacuum drying means, the water being removed through the layer of leather. Such known vacuum drying means are devices of the type used in the wet stage of tanneries for drying the leather from the still dripping wet condition after the tanning process. The leather in a dripping wet condition is arranged between a heated steel plate forming a support base and a felt-like porous sheet material is pressed against the leather, the steam formed being sucked through the felt-like porous sheet material under the action of vacuum.
It is also known to provide a carrier layer with a cover layer of synthetic plastics material having hollow microspheres embedded therein.